scispace - formally typeset
Search or ask a question

Showing papers in "British Journal of Applied Physics in 1965"


Journal ArticleDOI
TL;DR: In this article, the constitutive equations for inelastic thixotropic fluids proposed by Moore and Hahn et al. and generalized into an equation of state F = η(λ, D)D and a rate equation dλ/dt = gD(λ and D) for both thixotropy and antithixotropic fluid were discussed.
Abstract: The constitutive equations for inelastic thixotropic fluids proposed by Moore and Hahn et al. and for antithixotropic fluids by Peter are generalized into an equation of state F = η(λ, D)D and a rate equation dλ/dt = gD(λ, D) for both thixotropic and antithixotropic fluids. The properties of these equations and restrictions on their functional forms are discussed. It is shown that thixotropy and antithixotropy can be defined by whether (∂gD/∂D)λ and (dλ/dD)e are negative or positive. The behaviour of the fluid is discussed in terms of simple shear flow and the relation of such behaviour to laminar shear flow is indicated. The behaviour is obtained by solving the constitutive equations together with D(t). This gives rise to a line in the (F, D, t) space, and not a surface as is generally believed. The Moore model of a thixotropic fluid is discussed quantitatively as an example. The ways by which the constitutive equations can be determined experimentally are described. The ways in which λ can be defined in terms of experimental results are discussed.

332 citations


Journal ArticleDOI
TL;DR: In this paper, a method was developed for calculating characteristic fluorescence corrections in all cases involving K and L lines, based on the formula derived by Castaing for the case of one K line exciting another K line.
Abstract: A method has been developed for calculating characteristic fluorescence corrections in all cases involving K and L lines, based on the formula derived by Castaing for the case of one K line exciting another K line. A modification to the original formula is proposed, which takes into account more recent work on K line intensities; also some simplifications are suggested which enable corrections to be calculated quickly. Measurements of the relative intensities of K and L lines have been carried out to provide the necessary data for calculating corrections for fluorescence involving K and L lines.

265 citations


Journal ArticleDOI
TL;DR: In this article, a method for using the Kramers-Kronig dispersion relations to evaluate optical and dielectric parameters of materials from normal incidence reflectance data when data over only a limited spectral range is available.
Abstract: A method is given for using the Kramers-Kronig dispersion relations to evaluate optical and dielectric parameters of materials from normal incidence reflectance data when data over only a limited spectral range is available. No assumptions are needed concerning the behaviour of the reflectance data outside the experimental range, and no extrapolations of data are required. As an example, the extreme ultra-violet reflectance data of potassium iodide is analysed by this method.

233 citations


Journal ArticleDOI
TL;DR: In this paper, the index matching technique of Giordmaine and Maker has been extended to include the more general three-wave interaction, and the effect of the symmetry properties of the second-order polarizability tensor on the strength of the phase matched output signal at particular azimuthal angles is discussed for all non-centro-symmetrical uniaxial crystal classes.
Abstract: The index matching technique of Giordmaine and Maker has been extended to include the more general three-wave interaction. Two fundamentally different experimental arrangements may be considered; one has the two low frequency waves in parallel polarizations and the other has these waves in orthogonal polarizations. The equations relating the phase matching angle in uniaxial crystals to the crystal birefringence, dispersion, and the frequencies of the three waves are given. These equations allow a cone of phase matched directions to be generated about the crystal optic axis. The effect of the symmetry properties of the second-order polarizability tensor on the strength of the phase matched output signal at particular azimuthal angles is discussed for all non-centro-symmetrical uniaxial crystal classes. The particular form of the second-order polarizability tensor for each of the uniaxial crystals is tabulated assuming that Kleinman's symmetry conjecture is valid.

224 citations


Journal ArticleDOI
TL;DR: In this article, the fraction of the electron beam absorbed in a film of given thickness, found by subtracting the sum of the transmitted and backscattered fractions from unity, may be corrected by a simple procedure to give the fraction absorbed in an equal thickness at the surface of a solid target.
Abstract: Measurements have been made of the fraction of an electron beam backscattered from thin films of copper and gold at incident energies from 5 to 25 kev. The results from very thin films indicate that approximately 50% of backscattering from a solid target must be due to single scattering. A comparison with existing theories shows that the results can be fitted by a combination of the single scattering treatment of Everhart and the albedo theory of Bothe, if recent experimental values of the electron range are inserted. A degree of agreement also obtains with the comprehensive theory of backscattering due to Dashen. The fraction of the electron beam absorbed in a film of given thickness, found by subtracting the sum of the transmitted and backscattered fractions from unity, may be corrected by a simple procedure to give the fraction absorbed in a layer of equal thickness at the surface of a solid target. The resulting electron distribution in depth is obtained for different incident energies; that for copper at 20 kev agrees fairly well with a Monte Carlo calculation. The fraction of the energy absorbed within given depth and the energy dissipated per unit thickness are similarly derived. The latter distributions are sharply peaked just below the surface. Those for 20 kev agree well with the computations of Spencer, but less closely with Ehrenberg and King's observations of cathodoluminescence in phosphors. Regarded as a depth-dose distribution, the curve for copper at 20 kev agrees in general form with the measurements of characteristic x-ray production made by Castaing and Descamps. But there are significant differences between the energy distributions for copper and gold at the same incident energy, and also between the distributions at 10 and 20 kev, which may have implications for electron probe microanalysis.

169 citations


Journal ArticleDOI
TL;DR: In this paper, a two-dimensional photoelastic model was used to confirm the existence of high shear stresses near the fiber ends, which peak to values greater than those predicted by theory.
Abstract: Theories predicting the magnitudes of shear stresses at the surface of a fibre embedded in an elastic matrix under load are available in the literature. A two-dimensional photoelastic model confirms the existence of high shear stresses near the fibre ends, which peak to values greater than those predicted by theory. The significance of this to fibre reinforced composites is discussed.

153 citations


Journal ArticleDOI
TL;DR: In this paper, a general treatment has been given of the time lag for diffusion in a multiple laminate ABCD, where each lamina is composed of a different material and Henry's law governs the distribution of diffusant between each pair of laminae.
Abstract: By a development of the method of Frisch a general treatment has been given of the time lag for diffusion in a multiple laminate ABCD... where each lamina is composed of a different material. The treatment relates to flow of heat or matter in laminated slabs, hollow cylinders or spherical shells, under conditions where the diffusion coefficients are independent of concentration in each lamina, and where Henry's law governs the distribution of diffusant between each pair of laminae. Several special cases have been treated numerically which demonstrate some properties of the time lag in laminates.

121 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that the nature and magnitude of electric discharges from polyethylene sheet to an earthed electrode are a function of the relative humidity of the atmosphere and of the size of the electrode.
Abstract: Electrostatic charge densities of 1·1-2·3 nc cm-2 can be generated over areas of polyethylene (polythene) sheet by rubbing. The nature and magnitude of electric discharges from the polyethylene sheet to an earthed electrode are a function of the relative humidity of the atmosphere and of the size of the electrode. The discharges change from corona to spark type if the radius of a hemispherical electrode is increased from 1 to 10 mm; with the latter-sized electrode the sparks can contain up to 0·23 μC of charge. Such sparks, which have an equivalent electrical energy of 0·67-0·92 mJ, can ignite flammable mixtures of coal gas, methane, acetone, methanol, toluene, cyclohexane and dioxane with air. For a fixed electrode system the incendivity of a spark is directly related to the electric charge in it.

104 citations


Journal ArticleDOI
TL;DR: In this article, a general expression for the Lorentz force in the molten tip of an arc electrode is derived from the surface integral of Maxwell stress, and its variation and effect during the formation and detachment of the tip are discussed.
Abstract: A general expression for the Lorentz force in the molten tip of an arc electrode is derived from the surface integral of Maxwell stress. The Lorentz force in typical situations is calculated and its variation and effect during the formation and detachment of the molten tip are discussed. Values much larger than those customarily associated with molten tips are seen to appear towards the end of the tip detachment cycle.

103 citations


Journal ArticleDOI
TL;DR: In this paper, a modified form of the expression derived by Hertz from classical elasticity theory for the indentation of a ball into a semi-infinite elastic medium is presented.
Abstract: The indentation of vulcanized rubber sheets of various thicknesses by rigid spherical indentors has been examined experimentally for a variety of conditions. The results are shown to fit a modified form of the expression derived by Hertz from classical elasticity theory for the indentation of a ball into a semi-infinite elastic medium.

91 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the observation, recording, and interpretation of a pre-breakdown phenomenon occurring in the liquid dielectric hexane, which is seen as a region of changed refractive index, and an optical Schlieren system and a high speed streak camera have been constructed and used to investigate its nature and in particular its rates of growth and decay.
Abstract: The paper describes the observation, recording, and interpretation of a pre-breakdown phenomenon occurring in the liquid dielectric hexane. The effect is seen as a region of changed refractive index, and an optical Schlieren system and a high speed streak camera have been constructed and used to investigate its nature and in particular its rates of growth and decay. From the results obtained a theory of breakdown of the point-plane electrode system is deduced and shown to explain the observed phenomena remarkably well. The region of disturbance itself is interpreted as a local heating which marks the extent of a weak plasma. This plasma forms at the point cathode, grows in size with time to span most of the electrode gap, and breakdown indicated by an arc finally ensues. From the plasma geometry it is estimated that the minimum field existing at the plasma boundary during breakdown is about five times greater than the mean applied field. Measurements of the rate of movement of the plasma boundary suggest that at these high fields electron mobilities are becoming field dependent and rising rapidly. The minimum breakdown field is estimated as about 620 kv cm-1 and the average electron mobility at this field is estimated as about 0.03 cm2 v-1 sec-1.

Journal ArticleDOI
TL;DR: In this article, a differential method of measuring small density changes based on Archimedes' principle is described, which does not depend upon the accurate matching of the mass of a dummy and specimen and is independent of the density of the liquid used.
Abstract: A differential method of measuring small density changes based on Archimedes' principle is described. The necessary temperature conditions are easy to achieve, the method does not depend upon the accurate matching of the mass of a dummy and specimen and is independent of the density of the liquid used. The formula derived is readily evaluated numerically. Using a standard analytical balance, density changes smaller than 1 part in 106 can be detected.

Journal ArticleDOI
TL;DR: The reliability of the diametrical compression of a disk with a small central hole as a technique for determining the tensile strength of rock is described in this article, and it is suggested that the disk dimensions should be standardized if the test is to be used as a routine method of determining the strength of a rock.
Abstract: The reliability of the diametrical compression of a disk with a small central hole as a technique for determining the tensile strength of rock is described. Experiments on rock and plaster show that failure occurs in tension and that the tensile strength is dependent upon the disk dimensions. Some justification is given for the application of elasticity theory to rock. It is suggested that the disk dimensions should be standardized if the test is to be used as a routine method of determining the tensile strength of rock.

Journal ArticleDOI
TL;DR: In this article, a method for using the Kramers-Kronig dispersion relations to evaluate optical and dielectric parameters of materials from reflectance data measured at 45? incidence is presented.
Abstract: A method is given for using the Kramers-Kronig dispersion relations to evaluate optical and dielectric parameters of materials from reflectance data measured at 45? incidence. The method requires only a single determination of the reflectance spectrum and is valid for incident light which is either polarized or completely unpolarized. As an example, the real and imaginary parts of the complex dielectric constant, n2 - k2 and 2nk respectively, are evaluated from the 45? reflectance spectrum of a single crystal of magnesium oxide and compared with the values obtained from normal-incidence data.

Journal ArticleDOI
TL;DR: In this paper, the authors derived a number of criteria which allow the systematic adaptation of a levitation apparatus to a certain experimental problem by varying the relevant parameters and verified the results experimentally.
Abstract: Approximate calculations were made in order to obtain the force exerted on a specimen and its power absorption in levitation melting. The influence of the electrical and geometrical parameters is discussed and the results were verified experimentally. It was possible to derive a number of criteria which allow the systematic adaptation of a levitation apparatus to a certain experimental problem by varying the relevant parameters.

Journal ArticleDOI
TL;DR: In this article, the terminal velocities of spheres falling in six flocculated china-clay suspensions have been measured, and corrections applied for the retarding effect of the walls of the containing vessel.
Abstract: The terminal velocities of spheres falling in six flocculated china-clay suspensions have been measured, and corrections applied for the retarding effect of the walls of the containing vessel. The drag experienced by a sphere in the Reynolds number range of 250 to 40 000 is explained in terms of an unsheared envelope of the suspension which surrounds the sphere and which decreases in diameter as the velocity increases, disappearing completely at a velocity which depends primarily upon the concentration of the suspension.

Journal ArticleDOI
TL;DR: In this paper, an experimental investigation of the thermionic emission properties of a rhenium tape coated with lanthanum hexaboride was carried out for demountable vacuum ionization gauges and mass spectrometers.
Abstract: This paper describes an experimental investigation of the thermionic emission properties of a rhenium tape coated with lanthanum hexaboride, and considers its usefulness as a low temperature emitter for demountable vacuum ionization gauges and mass spectrometers Methods of preparation and processing are described and measurements of the Richardson emission constants are given The poisoning of the emission by those gases generally found in vacuum systems has been studied and the extent to which the activity can subsequently be restored is described Measurements have also been made of the rate of evaporation of active material from the cathode surface

Journal ArticleDOI
TL;DR: In this paper, a simple approximate analysis for the gravity flow of a cohesionless bulk solid in a converging channel is presented, which departs from the classical approach of plasticity in that the velocity and the stress fields are coupled.
Abstract: A simple approximate analysis for the gravity flow of a cohesionless bulk solid in a converging channel is presented. The analysis departs from the classical approach of plasticity in that the velocity and the stress fields are coupled. This coupling enforces a unique solution for the flow rate. The analytical expression for the flow rate is compared with the theory of Brown and with experimental data of Deming and Mehring. Although the present analysis overestimates the flow rate, the results indicate that further, more realistic, analyses following the present approach would prove to be fruitful.

Journal ArticleDOI
TL;DR: In this paper, the crystal structure of MoS2 compounds with the general formula Mo1-xWxSe2-yTey has been determined by x-ray analysis.
Abstract: Compounds with the general formula Mo1-xWxSe2-yTey have been prepared and their crystal structure determined by x-ray analysis. Measurements near room temperature indicate that most of the phases, with a structure similar to MoS2, are p-type with a Seebeck coefficient in the range 100-750 μV degC-1 and with conductivities below 10-2 ohm-1 cm-1; those with the WTe2 type of structure, however, have Seebeck coefficients below 20 μV degC-1 and conductivities in the range 20-250 ohm-1 cm-1.

Journal ArticleDOI
TL;DR: In this article, it was shown that the current field characteristic of silver sulphide is non-linear and that switching can occur between a high-resistance and a low-reistance state.
Abstract: It has been found that the current-field characteristic of silver sulphide is non-linear and that switching can occur between a high-resistance and a low-resistance state. It is shown that this behaviour is consistent with the rapid rise of electrical conductivity with temperature in the β-phase and a discontinuous increase of conductivity by orders of magnitude when the transition to the α-phase occurs at 450°K. The low thermal conductivity of Ag2S allows a strong radial temperature gradient to exist in wires and thus assists in the formation of a core of high electrical conductance. Switching effects have also been observed in alloys of Ag2S with Ag2Se and Ag2Te.

Journal ArticleDOI
TL;DR: The electron spin resonance lines of nitrogen impurity in diamond found by Smith, Sorokin, Gelles and Lasher have been re-examined in special samples and at low energy densities as discussed by the authors.
Abstract: The electron spin resonance lines of nitrogen impurity in diamond found by Smith, Sorokin, Gelles and Lasher have been re-examined in special samples and at low energy densities. The new spectral lines found have been analysed into three new systems: (i) Two more pairs of weak lines were found nearer to the main nitrogen lines. These lines are attributed to 13C atoms in some of the next nearest neighbour positions to the substitutional nitrogen. The principal hyperfine axes of the lines attributed by Smith et al. to the 13C atoms basal to the nitrogen of the N-C bond are found to be approximately parallel to the nitrogen hyperfine axes. (ii) Weak lines occur half-way between the main nitrogen lines. They are shown to be due to the interaction of the small quadrupole moment of the nitrogen with the electric field gradient. (iii) The lines due to the 15N with a nuclear spin of I = ½ have also been identified.

Journal ArticleDOI
TL;DR: In this paper, it has been shown that the temperature coefficient of resistance of NiCr films on glass is a function of the Ni/Cr ratio, and a unique composition is possible for which the temperature coefficients of resistance is independent of sheet resistance.
Abstract: It has been found that the temperature coefficient of resistance of NiCr films deposited on glass is a function of the Ni/Cr ratio. The temperature coefficient of resistance is more negative for films with high Cr content, and a unique composition is possible for which the temperature coefficient of resistance is independent of sheet resistance. The results of using a wide range of alloy compositions are presented and discussed. Methods of depositing these films with a known composition are examined and it is shown that a flash evaporation technique is satisfactory. A suitable design of source is given.

Journal ArticleDOI
M J Wheeler1
TL;DR: In this article, an approach for the determination of the thermal diffusivity of a thin slab of material heated to incandescence by an electron beam is described, where the electron beam amplitude modulated to vary sinusoidally with time and the phase difference between the resulting temperature fluctuations of the two faces of the slab yields the thermal diffusion of the sample.
Abstract: Apparatus is described for the determination of the thermal diffusivity by Cowan's method of a thin slab of material heated to incandescence by an electron beam. The electron beam is amplitude modulated to vary sinusoidally with time and the phase difference between the resulting temperature fluctuations of the two faces of the slab yields the thermal diffusivity of the sample. Results obtained for the thermal diffusivity and hence the thermal conductivity of platinum, tantalum, molybdenum and tungsten are given. The Lorenz functions of all four metals were found to be constant over the temperature ranges studied. Thermal conductivity values determined for three types of graphite, indium oxide, uranium dioxide, a U-49 at.%C alloy and boron nitride are also given. Results obtained with the apparatus to date cover a range of thermal conductivities of from 0.02 to 1.1 w cm-1 degK-1 within various temperature ranges between 1200 and 3000°K.


Journal ArticleDOI
TL;DR: In this paper, the authors measured the refractive index of Y3Fe5O12 and Gd1.5Y 1.5O 12 and found that it was 2.168 ± 0.003 at 3.0 μm with a variation of the order of 5% between 1 and 6 μm.
Abstract: The refractive index has been measured by the method of minimum deviation on single crystals of Y3Fe5O12 and Gd1.5Y1.5Fe5O12. The index was found to be 2.168 ± 0.003 at 3.0 μm with a variation of the order of 5% between 1 and 6 μm. It is concluded that the Faraday rotation should vary in sympathy with the index in this region.

Journal ArticleDOI
TL;DR: The theory of the phase matching technique of Giordmaine and Maker as discussed by the authors has been extended to include four wave third-order interactions and the effect of the symmetry properties of the thirdorder polarizability tensor on the strength of phase matched output signal as a function of phase matching angle theta and azimuthal angle phi is evaluated for uniaxial crystals.
Abstract: The theory of the phase matching technique of Giordmaine and Maker et al has been extended to include four wave third-order interactions Three different experimental situations are considered, one with the three lower frequency waves polarized orthogonally to the fourth, one with two orthogonal to the fourth and one with one orthogonal to the fourth The equations relating the phase matching angle in uniaxial crystals to the crystal birefringence and the frequencies of the four waves are given These can be solved to give a cone of phase matched directions about the crystal optic axis The effect of the symmetry properties of the third-order polarizability tensor on the strength of the phase matched output signal as a function of phase matching angle theta and azimuthal angle phi is evaluated for uniaxial crystals Expressions are also given for cubic and isotropic groups although in these classes phase matching is, of course, not possible by the birefringence method The form of the third-order polarizability tensor is tabulated assuming Kleinman's symmetry conjecture to be valid

Journal ArticleDOI
TL;DR: In this paper, a cylindrical wall stabilized thermal arc column is analyzed and the response of the column to changes in current and voltage and to periodic and modulated functions is given.
Abstract: A cylindrical wall stabilized thermal arc column is analysed. The column is assumed to fill the stabilizing tube and linear relationships are also assumed between the temperature-dependent gas properties of internal energy, electrical conductivity, and integrated thermal conductivity. The analysis yields expressions for both the steady-state and transient column properties. The response of the column to changes in current and voltage and to periodic and modulated functions is given.

Journal ArticleDOI
TL;DR: In this paper, the authors used the heat pulse method for determining thermal diffusivity α to ascertain if it can be applied to determine thermal conductivity changes of graphite and ceramics under neutron irradiation.
Abstract: The heat pulse method for determining thermal diffusivity α is investigated to ascertain if it can be applied to determine thermal conductivity changes of graphite and ceramics under neutron irradiation. It is verified that heat losses and a finite pulse time effect alter the temperature-time curve for the specimen rear face. The variation of the parameter ω in the relationship α = ωL2/π2t1/2 is determined experimentally for t1/2 values in the range 0.002 to 16 sec. When considerable heat loss occurs a reliable diffusivity value can still be obtained from the relationship α = 0.48 L2/π2tx by measuring tx, the time axis intercept at zero temperature rise.

Journal ArticleDOI
TL;DR: A simple formula for the correction to be applied to the light scattering coefficient of dielectric spheres due to a small but finite angle of acceptance is derived and is found to be in accordance with measurements as discussed by the authors.
Abstract: A simple formula for the correction to be applied to the light scattering coefficient of dielectric spheres due to a small but finite angle of acceptance is derived and is found to be in accordance with measurements. The effects of multiple and dependent scattering are discussed and are shown to be avoidable in most cases, although careful control of flocculation is necessary. The effects of a wide spectral bandwidth are considered and are not always found to be negligible.

Journal ArticleDOI
TL;DR: In this paper, it was shown that a laser beam focused inside a sample of glass produces a superheated liquid, and that the resulting internal pressure can only be released by internal fracturing, and, in some cases, also by fragmentation of the sample.
Abstract: Results are described which suggest that a laser beam focused inside a sample of glass produces a superheated liquid, and that the resulting internal pressure can only be released by internal fracturing, and, in some cases, also by fragmentation of the sample. The evidence is that the Brillouin scattered energy, demonstrated by Chiao, Townes, and Stoicheff is necessary, but not sufficient, to explain the results.